Problem: $ { {-2} \times \left[\begin{array}{rrr}{2} & {-1} & {-1} \\ {-1} & {4} & {1}\end{array}\right] = {?} } $
Explanation: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rrr}{-2}\times{2} & {-2}\times{-1} & {-2}\times{-1} \\ {-2}\times{-1} & {-2}\times{4} & {-2}\times{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{-4} & {2} & {2} \\ {2} & {-8} & {-2}\end{array}\right]}$